The present application relates to communication systems and, more particularly, to a novel method for the reduction of synchronous fading effects in a time-diversity multiple-access (TDMA) communications system.
In a communications system environment, such as a mobile radio channel, a fade is said to have occurred if the received signal envelope drops below some predefined acceptable level. Synchronous fading is that situation where a plurality of signal fades occur with a relatively constant time periodicity, as, for example, may be related to speed of the vehicle in which the receiving radio telephone is carried. In such a synchronous fading situation, the signals received from a central station experience periodic fading at fairly constant time intervals and pose a serious problem if the fading occurs synchronously with the occurrence of the particular time slot, or an integral multiple of time slot occurrences, in which data for that particular channel is transferred such that the transmissions to/from a particular user suffer degradation and cannot be mitigated by interpolation techniques, techniques using forward error correction codes, or other high overhead error correction techniques. It is therefore highly desirable to provide a method for the reduction of synchronous fading effects, particularly in a TDMA communication system.